Polyurethane based synthetic leathers comprising nanoparticles and having improved peel strength

ABSTRACT

Disclosed herein are methods of producing externally stabilized, poromeric synthetic leathers having improved peel strength, the methods comprising: preparing a prepolymer from a mixture comprising at least one polyester polyol, at least one polyether polyol, at least one isocyanate and optionally in a solvent; mixing the prepolymer, water, and a first surfactant; optionally add a second chain extender to form a PUD; preparing a mixture comprising said PUD, at least one surfactant, and at least one thickener; frothing said mixture; applying the frothed mixture to a fabric and thereby forming a coated fabric; adjusting the thickness of the frothed mixture on the coated fabric; drying the coated fabric. Methods of improving the peel strength of poromeric synthetic leathers are also disclosed. Externally stabilized synthetic leathers having improved peel strength are also disclosed.

BACKGROUND OF THE INVENTION

Currently, most polyurethane (PU) synthetic leathers are made usingorganic solvents, such as dimethylformamide, methylethyl ketone (MEK)and toluene. These solvents vaporize during manufacture and postmanufacturing, which leads to potential health issues for themanufacturing staff, the end users of the synthetic leather, and theenvironment. As a result, the European standard for the solvent PU basedsynthetic leather was changed to require less than 10 ppm DMF in theleather. Making such leathers is a challenge using organic solvent basedmethodologies. As a result, the use of solvent free or water borne PU(also known as polyurethane dispersion or PUD) has received attention,as it uses little, if any, organic solvent.

PUD is an aqueous emulsion of PU particles in water having high solidcontent, small particle size, and prolonged stability (up to six monthsor longer). When making synthetic leather using PUD, the followinggeneral method is used: 1) PUD is frothed 2) the frothed PUD is appliedto a fabric, 3) the thickness of the frothed PUD is adjusted usingmethods known in the art, and 4) the now coated fabric is cured to forma synthetic leather having a poromeric layer. See U.S. Pat. No.7,306,825 for an example of this methodology.

Synthetic leather derived from PUD is similar to that made from PU andan organic solvent. It is breathable, and has good hand-feel. Moreimportantly, the PUD synthetic leather is low in volatile organiccompounds. Typically, the PUD in the PUD based synthetic leather is madeby combining a diisocyanate and a polyol. The resulting product is thendispersed in water to make the PUD. While such synthetic leathers havehigh solid content and nice hand feel, they have poor peel strength.Thus, it would be advantageous to develop a PUD based synthetic leatherthat had improved peel strength performance.

SUMMARY OF THE INVENTION

In one aspect, disclosed herein are methods for producing externallystabilized, poromeric synthetic leathers having improved peel strength,the methods comprising:

preparing a prepolymer from a mixture comprising at least one polyesterpolyol, at least one polyether polyol, at least one isocyanate andoptionally in a solvent;

mixing the prepolymer, water, and a first surfactant;

optionally add a second chain extender to form a PUD;

preparing a mixture comprising said PUD, at least one surfactant, and atleast one thickener;

frothing said mixture;

applying the frothed mixture to a fabric and thereby forming a coatedfabric;

adjusting the thickness of the frothed mixture on the coated fabric;

drying the coated fabric.

In another aspect, disclosed herein are methods of improving the peelstrength of poromeric synthetic leathers, the methods comprising:

preparing a prepolymer from a mixture comprising at least one polyesterpolyol, at least one polyether polyol, at least one isocyanate andoptionally in a solvent;

mixing the prepolymer, water, and a first surfactant;

optionally add a second chain extender to form a PUD;

preparing a mixture comprising said PUD, at least one surfactant, and atleast one thickener;

frothing said mixture;

applying the frothed mixture to a fabric and thereby forming a coatedfabric;

adjusting the thickness of the frothed mixture on the coated fabric;

drying the coated fabric.

In another aspect, poromeric, synthetic leathers having improved peelstrength made according to the aforementioned methods are also disclosedherein.

The PUD based synthetic leathers disclosed herein are externallystabilized, i.e., they require the presence of at least one surfactantthat does not react with the PUD. Likewise, the methods disclosed hereinutilize externally stabilized PUDs.

The PUD based synthetic leathers disclosed herein may be used to makesynthetic leather for any leather or synthetic leather applications.Particular examples include footwear, handbags, belts, purses, garments,furniture upholstery, automotive upholstery, and gloves.

DESCRIPTION OF THE FIGURES

FIG. 1 is a picture of the cross section of a polyester polyol freesynthetic leather, where the coated fabric has long fibers (Control 1).

FIG. 2 is a picture of the cross section of a polyester polyol freesynthetic leather, where the coated fabric has short fibers (Control 2).

FIG. 3 is a picture of the cross section of a polyester polyolcontaining synthetic leather, where the coated fabric has long fibers(Example 1).

FIG. 4 is a picture of the cross section of a polyester polyolcontaining synthetic leather, where the coated fabric has short fibers(Example 2).

DETAILED DESCRIPTION

The methods and leathers disclosed herein require the incorporation ofat least one polyester polyol, at least one polyether polyol and atleast one isocyanate into the PUD.

Polyester polyols, are compounds that have an ester containing backboneand further comprise at least two OH groups. They are typically madefrom aliphatic organic dicarboxylic acids with 2 to 12 carbons,preferably aliphatic dicarboxylic acids with 4 to 6 carbons, andmultivalent alcohols, preferably diols, with 2 to 12 carbons. Examplesof aliphatic dicarboxylic acids include succinic acid, glutaric acid,adipic acid, suberic acid, azelaic acid, sebacic acid,decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid,isophthalic acid, and terephthalic acid. The corresponding dicarboxylicacid derivatives may also be used such as dicarboxylic acid mono- ordi-esters of alcohols with 1 to 4 carbons, or dicarboxylic acidanhydrides. Examples of divalent and multivalent alcohols, especiallydiols, include ethanediol, diethylene glycol, glycerine andtrimethylolpropanes or mixtures of at least two of these diols.Polyester polyols derived from vegetable oils (natural oil polyols orNOPs) may also be used.

Polyether polyols are compounds that have an ether backbone and furthercomprise at least two OH groups. Polyether polyols are commonly made byreacting monomeric compounds (either alone or in combination), such asglycerine (a triol), pentaerythritol (a tetraol), ethylene glycol (adiol), diethylene glycol (a diol of the formula: HOCH₂CH₂OCH₂CH₂OH),and/or sucrose with ethylene oxide, propylene oxide and/or butyleneoxide in the presence of an initiator and/or a catalyst. Suitableinitiators include aliphatic and aromatic amines, such asmonoethanolamine, vicinal toluenediamines, ethylenediamines, andpropylenediamine. Useful catalysts include strong bases, such as NaOH,or KOH, and double metal cyanide catalysts, such as zinchexacyanocobalt-t-butanol complex. Common polyether polyols includepolyethylene glycol (PEG), polypropylene glycol, and poly(tetramethleneether)glycol.

The use of a strong base catalyst to make a polyether polyol oftencauses the polyether polyol to be too basic, which has a detrimentaleffect on the aforementioned prepolymer. Consequently, it is oftennecessary to treat the polyether polyol with a scavenger compound, whichreacts with the residual base and makes the prepolymer more acidic.Suitable scavenger compounds include benzoyl chloride, and 85%phosphoric acid, with benzoyl chloride being preferred. Typically,adding aqueous acids introduces excess water into the prepolymer, whichwill react with the isocyanate and adversely impact the resultingleather. The inventors typically use a scavenger compound to adjust thenet controlled polymerization rate of the mixture to be lower than −10.ASTM D 6437-05 corresponds to the CPR procedure.

The isocyanates used herein contain at least two isocyanate groups andinclude organic diisocyanates, which may be aromatic, aliphatic, orcycloaliphatic, or a combination thereof. Representative examples ofsuitable diisocyanates include 4,4′-diisocyanatodiphenylmethane,2,4′-diisocyanatodiphenylmethane, isophorone diisocyanate, p-phenylenediisocyanate, 2,6 toluene diisocyanate, polyphenyl polymethylenepolyisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane,1,4-diisocyanatocyclohexane, hexamethylene diisocyanate, 1,5-naphthalenediisocyanate, 3,3′-dimethyl-4,4′-biphenyl diisocyanate,4,4′-diisocyanatodicyclohexylmethane,2,4′-diisocyanatodicyclohexylmethane, and 2,4-toluene diisocyanate, orcombinations thereof. More preferred diisocyanates are4,4′-diisocyanatodicyclohexylmethane, 4,4′-diisocyanatodiphenylmethane,2,4′-diisocyanatodicyclohexylmethane, and2,4′-diisocyanatodiphenylmethane. Most preferred are isophoronediisocyanate; 4,4′-diisocyanatodiphenylmethane (also known as 4,4′-MDI);and 2,4′-diisocyanatodiphenylmethane (also known as 2,4′-MDI). Theisocyanates may be purified or part of a mixture of one or moreisocyanates. If an isocyanate is a solid, it may be melted and/ordissolved in a solvent before it is reacted with the at least onepolyester polyol and the at least one polyether polyol.

The PUDs disclosed herein are made by reacting at least one polyesterpolyol at least one polyether polyol and at least one isocyanate,optionally in a solvent (wherein the solvent does not or minimallyreacts with the isocyanate). This affords a prepolymer, which is thenadded to a mixture comprising a solvent that is comprised of water, atleast one surfactant, and at least one chain extender. The mixture maybe stirred or mixed using methods known in the art. The resultingpolyurethane dispersion (PUD) has a “milk-like” appearance. Thepolyester polyol to the polyether ratio in the PUD is 0.1-99 polyesterpolyol to 99.9-1 polyether polyol. More preferably, the ratio is 30-70polyester polyol to 70-30 polyether polyol. The polyester:polyetherratio in the PUD is 1:0.5-4:0. More preferably the ratio is 1:0.5-2.5.

Typically, the ratio of the polyol mixture to the isocyanate is 85:15 to55:45. More preferably, the ratio is 75:25 to 65:35.

As will be appreciated by those skilled in the art, the order of mixingthe aforementioned reagents may be changed.

As used herein, a polyurethane dispersed in water is referred to as aPUD. When a polyurethane is dispersed in water, it is understood thatthe water optionally further comprises other, additional solvents, suchas ketones, C₁-C₆ alcohols, ethers, polyethers, DMF, dipropylene glycoldimethyl ether, and NMP. The water may contain one or more than oneadditional solvent. Preferably, these additional solvents comprise less10% by weight, based on the weight of the water and the additionalsolvent or solvents. More preferably they comprise less than 5% byweight. Still more preferably, it is less than 1% by weight. Mostpreferably, non-water solvents are not present in PUD. And whiledeionized and/or distilled water may be used, it is not required.

The leathers and methods of making the leathers disclosed herein,optionally further comprise an additive that is a; fillers (such as woodfibers, CaCO₃, SiO₂, and TiO₂), a flame retardant, a pigment, a flowingadditive, handfeel additive, antioxidant, anti-UV additive, antistaticagent, antimicrobial agent, or combinations thereof. Wood fibers alsoinclude wood floor. In one embodiment, the leathers and methods requirethe presence of at least one of the aforementioned additives.

The aforementioned fillers, when present, account for 0.1-50% by weightof the composition (excluding the fabric). More preferably, whenpresent, the fillings account for 0.1-40% by weight of the composition.Still more preferably, the fillers account for 0.1-30% by weight of thecomposition.

The non-filler additives, i.e., the aforementioned additives, notincluding the fillers, typically account for 0.01-20% by weight of thecomposition. More preferably, the non-filler additives account for0.1-10% by weight of the composition. Still more preferably, thenon-filler additives account for 1-5% by weight of the composition.Flowing additives, handfeel additives, antioxidants, anti-UV additives,antistatic agents, and antimicrobial agents are typically comprise lessthan 5% by weight of the composition. The additives may be added to thepolyester polyol modified PUD, to the mixture comprising the polyesterpolyol modified PUD or combinations thereof.

Examples of suitable surfactants used in the leathers and methodsdisclosed herein include, cationic, anionic, or nonionic surfactants.Suitable classes of surfactants include, but are not restricted to,sulfates of ethoxylated phenols such aspoly(oxy-1,2-ethanediyl)-α-sulfo-ω-(nonylphenoxy)ammonium salt; alkalimetal fatty acid salts such as alkali metal oleates and stearates;polyoxyalkylene nonionics such as polyethylene oxide, polypropyleneoxide, polybutylene oxide, and copolymers thereof; alcohol alkoxylates;ethoxylated fatty acid esters and alkylphenol ethoxylates; alkali metallauryl sulfates; amine lauryl sulfates such as triethanolamine laurylsulfate; quaternary ammonium surfactants; alkali metal alkylbenzenesulfonates such as branched and linear sodium dodecylbenzene sulfonates;amine alkyl benzene sulfonates such as triethanolamine dodecylbenzenesulfonate; anionic and nonionic fluorocarbon surfactants such asfluorinated alkyl esters and alkali metal perfluoroalkyl sulfonates;organosilicon surfactants such as modified polydimethylsiloxanes; andalkali metal soaps of modified resins. Exemplary surfactants includedisodium octadecyl sulfosuccinimate, sodium dodecylbenzene sulfonate,sodium alpha olefin sulfonate, sodium stearate, cocamidopropyl betaine,and ammonium stearate. Typically the total amount of surfactant used isless than 10%, based on the total weight of the dried synthetic leather.When the surfactant is mixed with the PUD, it is used to stabilize theair bubbles in the frothed PUD. The surfactant or surfactants aresometimes used as a concentrate in water. When two or more surfactantsare being used, they may be added to the mixture simultaneously or oneafter the other.

At least one thickener is added to the PUD before it is frothed.Thickeners are well known in the art and any thickener may be used inthe leathers and methods disclosed herein. The thickener may benon-associative or associative. It may be a cellulose ether derivative,natural gum alkali swellable emulsion, a clay, an acid derivative, anacid copolymer, a urethane associate thickener (UAT), a polyether ureapolyurethane (PEUPU), a polyether polyurethane (PEPU) or ahydrophobically modified ethoxylated urethane (HEUR). One preferredthickener is based on an acrylic acid copolymer, with ethylene acrylicacid copolymer (which is sold by The Dow Chemical Company as ACUSOL810A) being particularly preferred. Preferably, the thickener does notcause the PUD containing mixture to become unstable. If desired, acombination of thickeners may be used.

Examples of thickeners include those that do not cause the dispersion tobecome unstable. More preferably, the rheological modifier is a watersoluble thickener that is not ionized. Examples of useful thickenersinclude methyl cellulose ethers, alkali swellable thickeners (e.g.,sodium or ammonium neutralized acrylic acid polymers), hydrophobicallymodified alkali swellable thickeners (e.g., hydrophobically modifiedacrylic acid copolymers) and associative thickeners (e.g.,hydrophobically modified ethylene-oxide-based urethane blockcopolymers). Preferably the rheological modifier is a methylcelluloseether. The amount of thickener may be any useful amount. Typically theamount of thickener is at least about 0.1% to about 10% by weight of thetotal weight of the dispersion. Preferably the amount of thickener isbetween about 0.5% to about 7% by weight.

Chain extenders are bifuncational or polyfuncational, low molecularweight (typically weighing from 18 up to 500 g/mol) compounds thatcontain at least two active hydrogen containing groups. Any chainextender known to be useful to those of ordinary skill in the art ofpreparing polyurethanes can be used in the leathers and methodsdisclosed herein. Examples of chain extenders include diols, polyols,diamines, polyamines, hydrazides, acid hydrazides, and water. Of these,amine containing chain extenders and water are preferred. Furthermore,one or a combination of chain extenders may be used. For example, thechain extender may be mixed with or otherwise contain water.

Examples of chain extenders include water, piperazine,2-methylpiperazine; 2,5-dimethylpiperazine; 1,2-diaminopropane;1,3-diaminopropane; 1,4-diaminobutane; 1,6-diaminohexane, isophoronediamine, mixtures of isomers of 2,2,4- and 2,4,4-trimethyl hexamethylenediamine, 2-methyl pentamethylene diamine, diethylene triamine,dipropylenetriamine, triethylenetetramine, 1,3- and 1,4-xylylenediamine, a,a,a′,a′-tetramethyl-1,3- and -1,4-xylylene diamine and4,4′-dicyclohexylmethanediamine,3,3′-dimethyl-4,4′-dicyclohexylmethanediamine, 1,2-cyclohexanediamine,1,4-cyclohexanediamine, dimethylethylene diamine, hydrazine or adipicacid dihydrazide ethylene glycol; aminoethylethanolamine (AEEA);aminopropylethanolamine, aminohexylethanolamine;aminoethylpropanolamine, aminopropylpropanolamine,aminohexylpropanolamine; cyclohexane dimethanol; ethanolamine;diethanolamine; piperazine, JEFFAMINE D-230 (a polyether with two aminoterminating groups, having a molecular weight of approximately 230 thatis sold by the Huntsman Co.), methyldiethanolamine;phenyldiethanolamine; diethyltoluenediamine, dimethylthiotoluenediamineand trimethylolpropane. Particularly preferred chain extenders includewater, AEEA, piperazine and 1,4-diaminobutane.

Examples of pigments, include TiO₂, carbon black and other, knownpigments. Pigments are well known in the art and typically present inless than 20% by weight, based on the dried leather.

Examples of flame retardants that may be used in the leathers andmethods disclosed herein include those typically used to give enhancedflame retardant properties to a typical latex foam. Such flameretardants include phosphonate esters, phosphate esters, halogenatedphosphate esters or a combination thereof. Representative examples ofphosphonate esters include dimethylphosphonate (DMMP) and diethylethylphosphonate (DEEP). Representative examples of phosphates estersinclude triethyl phosphate and tricresyl phosphate. When used thephosphonate or phosphate ester flame retardants are present in the finalfoam at a level of from 0.5 to 30 percent by weight of the final foam.

Representative examples of halogenated phosphate esters include2-chloroethanol phosphate (C₆H₁₂Cl₂O₄P); 1-chloro-2-propanol phosphate[tris(1-chloro-2-propyl)phosphate] (C₉H₁₈Cl₃O₄P) (TCPP);1,3-Dichloro-2-Propanol Phosphate (C₉H₁₅Cl₆O₄P) also calledtris(1,3-dichloro-2-propyl)phosphate; tri(2-chloroethyl)phosphate;tri(2,2-dichloroisopropyl)phosphate; tri(2,3-dibromopropyl)phosphate;tri(1,3-dichloropropyl)phosphate; tetrakis(2-chloroethyl)ethylenediphosphate; bis(2-chloroethyl) 2-chloroethylphosphonate; diphosphates[2-chloroethyl diphosphate]; tetrakis(2-chloroethyl)ethylenediphosphate;tris-(2-chloroethyl)-phosphate, tris-(2-chloropropyl)phosphate,tris-(2,3-dibromopropyl)-phosphate, tris(1,3-dichloropropyl)phosphatetetrakis(2-chloroethyl-ethylene diphosphate andtetrakis(2-chloroethyl)ethyleneoxyethylenediphosphate. When used as aflame retardant, the halogenated phosphate ester will comprise 0.5 to 30percent by weight of the final foam.

Dehydratable flame retardants, such as alkali silicates, zeolites orother hydrated phosphates, borosilicates or borates, alumina hydroxides,cyanuric acid derivatives, powdered melamine, graphites, mica,vermiculites, perlites, aluminohydrocalcite, hydromagnesite, thaumasiteand wermlandite. Al₂O₃H₂O, and Alumina trihydrate, may also be used.

The dehydratable flame retardant is generally added to the polyurethanedispersion in an amount of from 5 to 120 parts per 100 parts dispersionsolids of the final Compound. Preferably the flame retardant is added inan amount from 10 to 100 parts per 100 parts dispersion solids of thefinal Compound. More preferably the flame retardant is added in anamount from 20 to 80 parts per 100 parts dispersion solids of the finalCompound.

Examples of hand feel additives include organic silicon compounds. Whenpresent, the amount of hand feel additive is 0.1% to about 10% by weightof the total weight of the dispersion. Preferably the amount of handfeel additive is between about 0.5% to about 5% by weight. In anotherembodiment, it is less than 3% by weight.

Antioxidants are known in the art and include polymeric hindered phenolresins.

In an embodiment according to any of the preceding aspects and/orembodiment(s), the synthetic leathers and methods described hereinfurther comprise at least one additive that is CaCO₃, SiO₂, wood fibers,TiO₂, or combinations thereof.

In another embodiment of any of the previously described aspects and/orembodiments, the mixture further comprises at least one additive that isa flame retardant, a pigment, a flowing additive, hand feel additive,antioxidant, anti-UV additive, or combinations thereof. Typically, theseadditives comprise 0.01 to 10% by weight of the solid content. Morepreferably, these additives comprise 0.1-8% by weight (still morepreferably, 2-5%) of the solid content.

Frothing may be accomplished by any method known in the art. Examplesinclude mechanical mixing, bubbling a gas into the mixture or acombination thereof.

Likewise, applying the frothed mixture to the fabric may also beaccomplished by any method known in the art.

The synthetic leathers and methods described herein utilize a fabricthat is coated with the frothed mixture. Many different fabrics that areknown in the art may be used. The fabric may be woven or nonwoven. Inone embodiment, the fabric is a non-woven fabric. The fabric may be madeby any suitable method such as those known in the art. The fabric may beprepared from any suitable fibrous material, such as, but not limitedto, synthetic fibrous materials and natural or semi synthetic fibrousmaterials and mixtures or blends thereof. Examples of synthetic fibrousmaterials include polyesters, polyamides, polyacrylics, polyolefins,polyvinyl chlorides, polyvinylidene chlorides, polyvinyl alcohols andblends or mixtures thereof. Examples of natural semi-synthetic fibrousmaterials include cotton, wool and hemp.

One preferred fabric is needled cotton and polyester fiber hybrid wovenfabric having short fibers (less than 1 mm) on the surface.

Another preferred fabric is needled cotton and polyester fiber hybridwoven fabric having long (greater than 3 mm) fibers on the surface.

In the leathers and methods disclosed herein, the fabric is optionallyimpregnated with a polymer resin. Acceptable resins include isocyanatecontaining resins, such as polyisocyanates (which contain at least twoisocyanate groups) were discussed above.

The impregnation of the fabric may be conducted by any suitable methodknown in the art. Examples include dipping, spraying or doctor blading.After impregnating, the impregnated textile may have excess resinremoved to leave the desired amount of dispersion within the textile.Typically, this may be accomplished by passing the impregnated textilethrough rubber rollers.

Generally, the impregnated fabric is impregnated with a resin in anorganic solvent (which makes a solution) or water (which makes adispersion). Typical solvents include dimethylformamide (DMF),methylethyl ketone (MEK) and toluene, although other solvents willafford acceptable results. Generally, the organic solvent used toimpregnate the fabric will contain 0.5-50% by weight of resin. Morepreferably, the organic solvent will contain 5-30% by weight of resin.Still more preferably, 15-25% by weight of resin.

If the fabric is impregnated with a resin in an organic solvent, thentypical solvents include dimethylformamide (DMF), methylethyl ketone(MEK) and toluene, although other solvents will afford acceptableresults. Generally, the organic solvent used to impregnate the fabricwill contain 0.5-50% by weight of resin. More preferably, the organicsolvent will contain 5-30% by weight of resin. Still more preferably,15-25% by weight of resin.

The frothed mixture may be applied to the fabric using any suitablemethod known in the art. Examples include using a Labcoater type LTE-S(Werner Mathic AG).

Likewise, the thickness of the froth on the fabric can be adjusted usingmethods known in the art. Examples include using a doctor bladeassembly.

The methods require drying or otherwise treating/curing the coatedfabric (i.e., the optionally impregnated fabric that is coated with thefrothed mixture) so that the synthetic leather forms. Suitable dryingconditions include subjecting the froth coated fabric to 1) a constanttemperature until dry, 2) a temperature gradient wherein the temperaturechanges over time, or 3) a multistep drying regime where the temperatureis held for a set amount of time and then changed to a differenttemperature, which is then held for a set amount of time (3, 4, 5, ormore drying steps may also be used). The drying times for each step maybe the same or different. Typical drying times are from a few seconds upto one hour. One example of a suitable drying protocol is to subject thefroth covered, optionally impregnated fabric to a temperature that is atleast 80° C. and no more than 250° C. More preferably, the optionallyimpregnated fabric is heated to a temperature of 80-105° C. for 4-10minutes and then to a temperature of 165-175° C. for 3-10 minutes.During the drying process, the water evaporates and the polyolefin sets(which may include melting of at least some of the material coated ontothe fabric) and thereby forms the final coating. The drying processshould not cause decomposition of any of the synthetic leathercomponents.

Typically, the drying is performed in an oven at atmospheric pressure,but it can be performed at pressures above or below atmosphericpressure.

In one embodiment, the polyester polyol modified PUD, the filler orfillers, and the other additives comprise 0.1-99.9% by weight of thetotal composition. More preferably, they comprise 60-99.9% by weight ofthe total composition. Still more preferably, 70-99.9% by weight of thetotal composition.

General Procedure for the Preparation of PUD Based, Poromeric SyntheticLeather Preparation of the Prepolymer:

Put at least one isocyanate resin into the reactor. If a resin is asolid, heat it until it is melted.

Combine the polyols in a separate reaction vessel. If the polyol mixtureis a solid at ambient temperature, heat the polyol mixture to atemperature higher than the mixture's melting point. Adjust thenet-controlled polymerization rate (CPR) to be lower than −10 using ascavenger compound, such as benzoyl chloride. Combine the polyol mixtureand the isocyanate(s). Stir and heat the combined mixture. Test the NCO% periodically using ASTM method ASTM D 2572-87. When the desired NCOcontent is reached, reduce the temperature of the reaction mixture.

Preparation of the Polyurethane Dispersion (PUD):

The prepolymer (from above) was placed in a plastic jar. The jar wassecured and a Cowles blade was inserted into the prepolymer such thatthe blade is just covered. At least one surfactant is added to theprepolymer, with mixing at 3000 rpm. Cold (˜5° C.) deionized water (DIwater) is slowly added to the mixture. Gradually, the water-in-oilemulsion is converted into an oil-in-water dispersion. A solution ofchain extender in DI water is slowly fed into the dispersion, the finaldispersion is allowed to degas under ambient condition with randomstirring.

Experimental Procedures

The following three PUDs were used in the examples.

TABLE 1 PUD type Type PUD 1 PUD 2 PUD 3 Materials Syntegra 3000Polyester polyol Polyester polyol containing PUD containing PUD CompanyDow Synthesis Synthesis Solid content/% 50-55 50-55 50-55 Polyester/0/70/30 22.6/47.4/30 41/29/30 Polyether/ Isocyanate Ratio ParticleSize/μm 0.3 1.9 0.8

Note: PUD 1 is the control because it does not contain any polyesterpolyol. PUDs 2 and 3 contain polyester polyol and were made according tothe methods described herein. The polyester in PUD 2 was Bester 127 (apolyester polyol having an Mn of about 2,000, sold by The Dow ChemicalCompany), and the polyester in PUD 3 was Bester 48 (a polyester polyolproduct with an Mn=1000, sold by The Dow Chemical Company). Thepolyethers in all these three PUDs were mainly VORANOL 9287A (a 2000molecular weight, 12 percent ethylene oxide capped diol stabilized withalkyldiphenylamine, a product of The Dow Chemical Company) with somesmall dosage polyether resins (Mn=approximately 2000, sold by The DowChemical Company) and CARBOWAX™ Methoxy polyethylene Glycol (MPEG) 1000(from The Dow Chemical Company) mixture. The isocyanate was4,4′-Methylenediphenyl diisocyanate (MDI) from Huntsman.

The following two fabrics were used in the examples below.

TABLE 2 Fabric type Impregnated with Type Description Resin? Fabric 1Needled cotton and polyester fiber No hybrid woven having long (>3 mm)fibers on the surface fabric Fabric 2 Needled cotton and polyester fiberNo hybrid woven fabric with shorter fibers (<=1.2 mm) on the surface

Preparation of the Control Samples:

A poromeric layer of the synthetic leather was made using frothed PUD.The frothing PUD dispersion had a solids content of 50-55 percent byweight with ammonium stearate (STANFAX 320, Para-chem), disodiumoctadecyl sulfosuccinimate (STANFAX 318, Para-chem), cocamidopropylbetaine (STANFAX 590, Para-chem) and acrylic acid copolymer thickener(ACUSOL 810A, Dow). The thickened PUD viscosity was controlled to 13,000cp to 28,000 cp. The detailed PUD formulations appear in Table 3.

The PUD was frothed using a Model 2MT1A foam machine (E.T. OAKES Corp.)run at 1000 rpm. The wet froth density of the PUD was about 0.50-0.85g/cm³. A Labcoater type LTE-S (Werner Mathic AG) was used to apply thefrothed PUD to a fabric that was attached to pin frame. The doctor knifewas positioned at 1.8-2.5 mm between the roller and knife (includingresin and fabric). The frothed dispersion was dispersed and the doctorbladed to foam a coating of frothed PUD on the fabric. The coated fabricwas then placed in an oven at 100° C. for 6-10 min, which was thenheated to 170° C. in about 5 min. to form the synthetic leather having aporomeric layer.

TABLE 3 PUD poromeric layer formulation Items Control 1 Control 2Materials Weight/g Weight/g Fabric type Fabric 1 Fabric 2 PUD 1(Syntegra 3000) 1000 1200 Stanfax 320 40.0 48.0 Stanfax 590 11.3 13.5Stanfax 318 13.1 15.6 Acusol 810A 60.0 79.4 Viscosity/cp 17900 23300Foam density/(g/cm³) 0.748 0.690

Preparation of the Experimental Examples

The polyester polyol modified PUD based leathers were made essentiallyaccording to the methods described above for the control samples. Thekey difference being the use of the formulations and fabrics in Table 4replacing those in Table 3.

TABLE 4 Polyester modified PUD poromeric layer formulation Sample 1Sample 2 Materials Weight (g) Weight (g) Fabric type Fabric 1 Fabric 2PUD 2 1000 — PUD 3 — 750 Stanfax 320 (ammonium stearate) 40.0 30.2Stanfax 590 (cocamidopropyl betaine) 11.3 10 Stanfax 318 (disodiumoctadecyl 13.1 9.5 sulfosuccinimate) Acusol 810A (acrylic acidcopolymer) 76.5 77.3 Viscosity (cp) 17500 17200 Foam density (g/cm³)0.781 0.622

Peel Strength Test:

Peel strength tests were conducted according to the GB/T 8949-2008Chinese Standard. Briefly, the synthetic leather was cut into two 15cm×12 cm leather sheets. Then these two leather sheets were gluedtogether using a suitable adhesive, but about 5 cm (in the lengthdirection) was not treated with adhesive. The two pieces were pressedwith a 5 Kg steel plate, dried and cured over 24 hours. The bonded sheetwas cut along the length-wise into four 15 cm×3 cm samples. These foursamples were tested using an Instron machine with a speed of 200 cm/min.

PUD Viscosity Measurement

Bulk viscosities of the thickened PUD before frothing were measuredusing a Brookfield viscometer with a 20 rpm #6 spindle.

Results of Leather Peel Strength:

TABLE 5 Peel strength of the poromeric layer samples Items Control 1Control 2 Sample 1 Sample 2 Peel strength/(N/(3 cm)) 28 46 52 90 FabricFabric 1 Fabric 2 Fabric 1 Fabric 2

The peel strength increased from 28 N/(3 cm) (Control 1) to 46 N/(3 cm)(Control 2) by changing from a fabric having long fibers on the surfaceto a fabric having short fibers on the surface. Replacing the PUDs inControl samples 1 and 2 with polyester polyol modified PUD (Sample 1 and2) afforded synthetic leathers having significantly improved peelstrengths, relative to PUDs that do not contain any polyester polyolmodified PUD.

Comparing Control 1 to Sample 1 shows the polyester polyol modified PUDhas a peel strength that is 85% higher than the correspondingnon-modified PUD. Likewise, Sample 2 has a peel strength that is 96%higher than the corresponding non-modified PUD

FIG. 1 (Control 1) and 3 (Example 1), both are cross sections ofsynthetic leathers on fabrics having long fibers, and they have similarstructures. Thus, Example 1, while having superior properties relativeto Control 1, has a similar overall structure. The same applies for FIG.2 (Control 2) and 4 (Example 2), but the fabrics contain short fibers.

What is claimed is:
 1. Methods for producing externally stabilized,poromeric synthetic leathers having improved peel strength, the methodscomprising: preparing a prepolymer from a mixture comprising at leastone polyester polyol, at least one polyether polyol, at least oneisocyanate and optionally in a solvent; mixing the prepolymer, water,and a first surfactant; optionally add a second chain extender to form aPUD; preparing a mixture comprising said PUD, at least one surfactant,and at least one thickener; frothing said mixture; applying the frothedmixture to a fabric and thereby forming a coated fabric; adjusting thethickness of the frothed mixture on the coated fabric; drying the coatedfabric.
 2. Methods of improving the peel strength of poromeric syntheticleathers, the methods comprising: preparing a prepolymer from a mixturecomprising at least one polyester polyol, at least one polyether polyol,at least one isocyanate and optionally in a solvent; mixing theprepolymer, water, and a first surfactant; optionally add a second chainextender to form a PUD; preparing a mixture comprising said PUD, atleast one surfactant, and at least one thickener; frothing said mixture;applying the frothed mixture to a fabric and thereby forming a coatedfabric; adjusting the thickness of the frothed mixture on the coatedfabric; drying the coated fabric.
 3. Methods according to claim 1,wherein the fabric is a needled cotton and polyester fiber hybrid wovenfabric having short fibers on the surface and is optionally impregnatedwith a polymer resin.
 4. Methods according to claim 1, wherein at leastone surfactant is ammonium stearate, disodium octadecyl sulfosuccinimateor cocamidopropyl betaine.
 5. Methods according to claim 1, wherein themixture comprises at least two surfactants.
 6. Methods according toclaim 1, wherein the mixture further comprises at least one additivethat is CaCO₃, SiO₂, wood fibers, TiO₂, a flame retardant, a pigment, aflowing additive, handfeel additive, antioxidant, anti-UV additive, orcombinations thereof.
 7. Methods according to claim 1, wherein the PUDhas a solid content of 30-65% by weight.
 8. Methods according to claim1, wherein the isocyanate comprises isophorone diisocyanate;4,4′-diisocyanatodiphenylmethane; 2,4′-diisocyanatodiphenylmethane, orcombinations thereof.
 9. Methods according to claim 1, wherein thepolyester:polyether ratio in the PUD is 1:0.5-4.
 10. Methods accordingto claim 1, wherein the coated fabric is dried/cured at a temperature ofat least 30° C. and no more than 200° C.
 11. Methods according to claim1, wherein the isocyanate comprised methylenediphenyl diisocyanate, andat least one polyester polyol has an Mn of 1000-2000.
 12. Methodsaccording to claim 1, wherein the thickening agent is an acrylic acidcopolymer.
 13. Methods according to claim 1, wherein the PUD is mixedwith at least three surfactants that are independently selected from thegroup consisting of disodium octadecyl sulfosuccinimate, sodiumdodecylbenzene sulfonate, sodium alpha olefin sulfonate, sodiumstearate, cocamidopropyl betaine, and ammonium stearate.
 14. Methodsaccording to claim 13, wherein the at least three surfactants areammonium stearate, disodium octadecyl sulfosuccinimate andcocamidopropyl betaine, and are in the ratio of 1:0.2-0.4:0.23-0.4. 15.A porometric synthetic leather made according to claim 15.